Colloid metallurgy

ABSTRACT

A process for producing non-porous full-density metal articles comprising forming a porous compact colloidal substantially pure metal particles having a maximum mean particle size of 0.2 micron, said metal being at least one metal selected from silver and the metals of groups IIIb, IVb, Vb, and VIII of the Periodic Table of the Elements, and then sintering said porous compact at a temperature substantially below the melting point of said metal and thereby forming a non-porous fully dense metal article within 10 minutes of initiation sintering, and maintaining said porous metal compact in a vacum or an inert atmosphere until said fulldensity metal article is formed.

United States Patent 11 1 Oka 1 Feb. 13, 1973 COLLOID METALLURGY 3,268,530 3/132 afidall unis/226 ,436. 2 1 2. 224 X [76] Inventor: Akira Oka, 71, l-chome, Sugamo, 3 0 en Toshimwku, Tokyo, Japan FOREIGN PATENTS OR APPLICATIONS [22] Filed; May 26, 1969 1,178,722 1/1970 Great Britain ..75 224 423,823 2/1935 Great Britain..... .,..75/224- [21] Appl. No.: 827,997 523,318 7/1940 Great Britain ..75/225 Related US. Application Data OTI-IER PUBLICATIONS [631 Continuation-impart of Ser. Nos. 611,253, Jan. 24, 1967, abandoned, and Ser. No. 714,076, March 18, 1968.

[30] Foreign Application Priority Data Jan. 25, 1966 Japan ..41/3885 [52] US. Cl. ..75/225, 75/211, 75/224 [51] Int. Cl. .L ..B22f 1/00 [58] Field of Search ..75/224, 225, 226, 214, 222, 75/21 1 I [56] ,References Cited UNITED STATES PATENTS 2,823,116 2/1958 Angier ..75/214 3,052,532 9/1962 Stoddard et a1. ...75/200 3,376,107 4/1968 Oka ..75/214 3,116,146 12/1963 Gatti ..75/214 1,174,646 3/1916 Williams ..75/214 2,807,082 9/1957 Zambrow ..75/224 X 2,818,339 12/1957 Dodds ..75/226 X 3,005,701 10/1961 Eberhardt .75/224 X 3,109,735 11/1963 Googin ..75/224 3,150,975 9/1964 Beaver..... ..75/224 X 3,216,824 11/1965 Boghen ...75/224 X 3,251,684 5/1966 Spacil ..75/224 X Yao, et a1; Nippon Kinzolu Gakkaishi Vol. 22, N0. 12, 1958 pp. 652-655.

Zima et al., International Journal of Powder Metallurgy 2(3) 1966 pp. 49-57.

Goetzel, Treatise on Powder Metallugy" Vol. I, (1949); pp. 431-432, 622-624.

Wilke, Be Processing by Powder Metallugy, Aug. 1961 Journal of Metals, pp. 540-543.

Primary Examiner-Carl D. Quarforth Assistant Examiner-B. H. Hunt Attorney-Flynn and Frishauf [57] ABSTRACT A process for producing non-porous full-density metal articles comprising forming a porous compact colloidal substantially pure metal particles having a maximum mean particle size of 0.2 micron, said metal being at least one metal selected from silver and the metals of groups 111b, IVb, Vb, and VIII of the Periodic Table of the Elements, and then sintering said porous compact atatemperature substantially belw the melting point of said metal and thereby forming a non-porous fully dense metal article within 10 minutes of initiation sintering, and maintaining said porous metal compact in a vacum or an inert atmosphere until said full-density metal article is formed.

14 Claims, No Drawings COLLOID METALLURGY The present application is a continuation-in-part of applicants pending United States application Ser. No. 611,253, filed Jan. 24, 1967, now abandoned and Ser. No. 714,076, filed Man-18,1968.

BACKGROUND OF THE INVENTION:

This invention depends upon a discovery of a new phenomena, that is, when colloidal metal particles having a virgin surface is heated in a protective atmosphere preferably in a vacuum a rapid matter displacement, which looks like a flow of a metal, is occurred within one minute, and non-porous metal, articles are 1 produced. This flow lilte phenomena was observed under a hot stage microscope.

The present invention relates to the process of heating colloidal metal particles which have a virgin surface for a few minutes, and more particulary to heating two dimensional plate or three dimensional compact made .of metals to obtain an article or plating which is as tered articles for a number of uses. It has previously been proposed to carry out the sintering step at a temperature which is so high that some of the components to be sintered will melt, i.e., the sintering temperature is at least as high as the melting point of at least one of the metals in a mixture of metals to be sintered. When a single metal was sintered, it was necessary to sinter at essentially the melting point of the metal to obtain dense pore-free products. Such processes give porefree products, but the article resulting therefrom is not really a sintered article, since the metal has gone through a liquid phase.

It is an object of the present invention to provide a new process in metallurgy, to manufacture heated articles or plating which have a density commensurate with the density of the metal itself, i.e., as if it had been melted. In addition to obtain non-porous plating or articles, porous plating or articles are obtained, when heat treatment is stopped before the flow" is occurred.

' BROAD STATEMENT OF INVENTION:

The present invention provides a process for producing porous or non-porous metal plates or articles comprizing forming a porous compact of colloidal metal particles having the maximum mean particle size of 0.2 micron, said colloidal metal particles being substantiallyfree of oxide on the surface thereof and then heat said porous compact at a temperature substantially below the melting point of said metal to obtain a porous or non-porous fully dense metal article for a few minutes. Said porous compact is formed and maintained in a non-oxidizing atmosphere and then heat in a non-oxidizing atmosphere for a few minutes.

DETAILED DESCRIPTION OF INVENTION:

It is important that the collidal particles of metal used in forming the fully dense metal article should have their surfaces substantially free of oxide (i) at the time the porous compact is formed, (ii) during the formation of the porous compact, (iii) during any subsequent storage period prior to sintering, and (iv) during the sintering operation. This oxide free surface is preferably obtained and maintained by utilizing metal particles produced by a process which yields particles having a surface free of oxide, and then maintaining said particles under non-oxidizing conditions. These non-oxidizing conditions during the formation of the porous compact preferably involve the use of an inert atmosphere or a vacuum atmosphere. Similarly, storage of the porous compact should be under non-oxidizing conditions such as vacuum or an inert atmosphere, or some other method of protecting the surface of the metal particles, such as impregnation of the porous compact with a low melting solid. Similarly, the heat operation must be carried out under non-oxidizing conditions, usually an inert atmosphere or vacuum.

The metal particles are formed into a porous compact before insertion into the heat furnace. The formation of the porous compact usually involves a pressing operation. Although hot pressing may be utilized, a major advantage of the present invention is that the process may utilize a pressing operation at ambient temperatures to obtain a pore-free fully dense metal product after heating. On the contrary, the prior art processes required either (i) a hot pressing operation at a temperature sufficiently high to melt the metal particles (or if a mixture of particles of different metals is being pressed, to melt at least some of the metal particles) or (ii) sintering at a temperature sufficiently high to melt metal as aforesaid. The term forming a porous compact" as used herein also includes positioning, e,g., pouring, metal particles in a shaped container to form a porous compact having the shape of the container, without the application of pressure.

The starting material for the process of the present invention is a colloidal metal, having a maximum mean particle size of 0.2 micron. For example, pure colloidal titanium. The colloidal titanium can be obtained by dehydrogenation of titanium hydride, of such a composition that it is exactly stoichiometric (TiH This dehydrogenated titanium can then be compacted at a substantial pressure, for example about 5 tons/cm in an atmosphere of an inert gas such as nitrogen, argon and the like. It may then heat for 5 minutes at a temperature of 1,200C. By this process, a product is obtained which is non-porous; and having a density of about 4.54 g/cm", which corresponds to the full density of metallic titanium. Similar results are obtained at lower sintering temperatures, e.g., l,100C.

The process of the present invention is applicable not only to titanium, but also to other metals. The metal colloids, forming the starting material, may be obtained either by decomposition of organic metal compounds, by de-hydrogenation as above referred to, and for example, by passing a high-voltage, high-frequency spark through metal pellets, while immersed in liquid ammonia as, for example, more specifically set forth in French Pat. No. 1,435,501, or Swedish Pat. No. 212,143, or Belgian Pat. No. 665,832, by reduction in a liquid phase and filtered and reduced by pure hydrogen at 2,300C for a few hours.

The process of the present invention includes compacting colloidal metal particles produced by decomposition of metal hydrides, or of organic metal compounds, or by a spark in an ammonia surrounding, or by reduction in a liquid phase. The compacting process is carried out in an oxygen-free atmosphere. A subsequent sintering step of the compacted bodie is likewise carried out in oxygenfree conditions, for example in a vacuum furnace. The resulting article will then have full density.

Decomposition of corresponding metal hydrides, to obtain colloidal particles, is a suitable step for use with transition metals, such as group lllb, lVb, Vb, lanthanide and actinide metals. Heat decomposition of corresponding metal carbonyls is a suitable process to obtain colloidal particles of group iron, nickel, cobalt, and group Vb, Vlb, and Vllb metals. Heat de-composition of corresponding alkoxides is a suitable process for use with group lVb, Vb, Vlb, Vllb and Vlll metals. The process set forth in the aforementioned French, Belgian and Swedish Patents is useful to obtain colloidal particles of any metal. Reduction in a liquid phase and rereduction by pure hydrogen to obtain colloidal particle of any metals.

As a starting colloidal particle, hydrides is best in order to obtain a virgin surface. In the other cases mentioned above, pre-treatment of reduction by pure hydrogen at at 2-300C for a few hours is preferable.

The inert gases used to replace oxygen during the compacting and sintering step, or to replace the ambient air containing the oxygen, are preferably of high purity. The purity of the gases will influence the heating process. ln case of colloidal particles produced from metal hydrides, cylinder nitrogen can be used; in other cases, argon having a dew-point of lC, and introduced in a vacuum of mmHg is suitable.

The heating temperature utilized in the present invention is substantially below the melting point of the metal. By excluding air, and particularly oxygen, the tendency of the colloidal metal particles to oxidize is eliminated. Investigation of the mechanism on a vacuum hot-stage microscope led to the observation that the porous compacts utilized in the present invention appear to flow for several ten seconds at temperatures substantially below the melting point of the metal particles, to achieve a fully dense pore-free metal articles. The temperature at which this phenomens occurs varies for different metals, but is substantially below the melting point of the metal. The surface of the colloidal metal particles must' be free of oxide. Thus, the flow-phenomena was not observed at pressures greater than 10'' mm of mercury. With titanium, it is strengthened alloys. The low sintering temperature, which can be used in the process of the present invention, is especially suitable for the production of nonporous alloys having high melting points.

The non-oxidizing atmospheres required in the process of the present invention include vacuum, and inert atmospheres, such as, nitrogen, hydrogne, and argon.

The process according to the present invention is applicable not only to the production of non-porous articles, but also porous articles which have a very fine pore. When heating process is stopped before the flow occures, such porous articles are obtained. In oilless bearing the finer the pore, the longer the life. So oil-less bearing made of such colloidal metal particle can be used for space use.

When the process according to the present invention is applied to two dimensional plate, filter plate which have very fine pore, and metal plating, for example, titanium and zirconium plating on other metal or substances are produced.

In a case of titanium plating, colloidal titanium hydride powder is painted on iron or steel by dispersing titanium hydride in pure alcohol. It is heat at l,O30C for 2 minutes in a vacuum maintained at 2X12 mmHg, and a non-porous titanium plating is obtained. The temperature of heat treatment is lower than the eutectic point of titanium and iron. In a case of zirconium plating, the temperature of heat treatment is 880C, this temperature is also lower than the eutectic point of zirconium and iron. In such lower temperature, flow is also observed by a hot-stage microscope.

EXAMPLE 1 Startingmaterial: titanium colloid obtained by heat de-composition of TiH A mass of sponge titanium (purity 99.9 percent by ASTM standard) is subjected to reaction with pure hydrogen. Degradation of the purity of the titanium, and of the hydrogen is avoided by utilizing a membrance of palladium during the purification step. A titanium hydride material, having a composition exactly TiH is thus obtained.

The thus obtained titanium hydride is milled for about 40 hours in a rotary mill made of sintered alumina. The hydride power is pulverized, to the particle size of between 60 to 300A. The particle size is determined by electron-microscopy. The hydride is then thermally dehydrated at 450C in a tube furnace evacuated to 2 X 10- mmHg. The thus obtained colloidal titanium has a specific surface of 16 m lg, from which a particle size of 0.08 micron, can be calculated. Residual hydrogen of 27.7 ppm is found, by the fusion method.

The obtained colloidal titanium is kept in an airtight container, filed with cylinder nitrogen, as it is quite phrophoric in air.

The colloidal titanium is then compacted; in accordance with the present invention, air and oxygen are excluded by compacting in nitrogen atmosphere. Compacting pressure is about 5 tons/cm? A disk of l 1.3 mm diameter, approximately 2-3 mm thick, and having a green density of 3.1 g/cm is obtained. This disk is impregnated with liquid paraffin to protect it from air. It is then heated at l,400C for 2 hours in a vacuum furnace, with a vacuum maintained at 5 X mmHg. The density of the product obtained is 4.54 g/cm", as measured by a picnometer. The structure is solid and non-porous, which can be observed by means of a microscope having a magnification of 400 X. When pure hydrogen is used instead of the nitrogen atmosphere, heating at 1,200C for 5 minutes produced a dense non-porous article. When colloidal titanium hydrides of above mentioned is used, a dense nonporous articles was produced by compacting in air, heating at 1,200C for 5 minutes.

EXAMPLE 2 Zirconium colloid is obtained by heat decomposition of ZrH j similar to the process of example 1, to obtain colloidal titanium.

Compacting and heating are substantially the same as those in example 1; except: Compacting in pure hydrogen, and at a heating temperature of 1,500C for 5 minutes. Result: a heated article is obtained having a density of 6.5g/cm EXAMPLE 3 Carbonyl nickel powder having a mean particle size of 0.02 micron is compacted in an argon atmosphere. Pressure: 7 tons/cm. The compressed article is heated in a vacuum furnace for five hours at 1,300C, with a vacuum of 10 mm Hg. Result: a heated article having a density of 8.9 g/cm.

When carbonyl nickel powder is reduced by pure hydrogen (dew point is lower than 70C) at 300C for 2 hours, heat treatment for 5 minutes at 1,300C is enough to obtained non-porousheated article.

EXAMPLE 4 Nickel colloidal particles are obtained by electrical sparking with 10,000 V, 50 kHz electric current of nickel pellets, on a nickel electrode, within liquied ammonia (details of this process are explained in the aforementioned French, Belgian and Swedish patents). The resulting powder is compacted in an atmosphere of argon under a pressure of 7 tons/cm? The compacted article is heated at 1,300C for a period of 10 hours in a vacuum of 10' mmHg. Result: a product having a density of 8.7g/cm When nickel colloidal particle thus obtained is reduced by pure hydrogen (dew point is lower than 70C) at 300C for two hours, heat treatment for 5 minutes at 1,300C in a vacuum of l0 mm1-1g is enough to obtained a non-porous product having a density of 8.9g/cm EXAMPLE 5 One gram of colloidal titanium particles having a mean diameter of 0.08 micron were placed in a sintered alumina cup and then, without any compaction, were placed in a vacuum furnace (2 X IO' mmHG) and heated at 1,150C for 5 minutes. The product had a density of 4.54 g/cm.

EXAMPLE 6 THROUGH 24 A comparison of Example 6 which is within the process of the present invention, and Examples 7 and 8 which differ in that larger particles of titanium were used, establishes the necessity for using the colloidal titanium particles, i.e., those having a maximum mean particle size of 0.2 micron. In similar fashion a comparison of Example 9 illustrating a process within the scope of the present invention. as contrasted with the product of Example 10 which is not fully dense, proves the criticality of using the colloidal particles. Examples 12, 13, 14, 15, 16, 17, 18, 22 and 24 further illustrate the advantages of the process of the present invention. in each case, the first of the paired group of experiments illustrates a process within the scope of the present invention and the latter 7, 8, 10, 13, 19,21, 23 illustrates the same process using a metal particle of a size larger than 0.2 micron. in each example using the larger particles,

articles which are not full density were obtained.

EXAMPLES 6 THROUGH 24 Mean radius of metal powder Start after Sinter ing decompo ed Sintered Example mater sition temp. time Sintered number metal ial micron C minutes density 6 Ti Til-1, 0.08 1,200 5 4.54 7 Ti TiH, 0.5 1,200 4.46 8 Ti TiH 200 1,200 120 4.38

mesh 9 Zr ZrH, 0.06 1,500 5 6.49 10 Zr ZrH, 0.6 1,500 120 6.34 11 Hf HFH, 0.1 1,800 5 13.0 12 V VH 0.2 1,400 10 6.10 13 V Vl-l 1 1,400 120 6.00 14 Sm Sml-l; 0.06 1,000 10 6.98 15 Eu EuH 0.12 950 10 5.24 16 Th Thl-l, 0.07 1,400 5 11.5 17 U UH; 0.06 900 5 19.0 18 Fe Fe 0.04 1,300 5 7.88

carbonyl 19 Fe Fe 1 1,300 120 7.32

carbonyl 20 Ni Ni 0.02 1,200 5 8.9

carbonyl 21 Ni Ni 0.2 1,300 120 8.71

carbonyl 22 Ag Ag 0 800 10.5 23 Ag Ag 1 800 120 10.4 24 Cu Cu 0.05 850 5 8.9

liquid phase reduction The above examples illustrate that the heated articles obtained, in accordance with the present invention, have specific gravities comparable to those of the metals themselves. The heated temperature used may be substantially below the melting point of the materials.

EXAMPLE 25 TITANIUM PLATlNG Colloidal titanium hydride particle is pained on a purified iron surface by dispersing titanium hydride in pure alcohol. After alcohol dried, it is heated at l030C for 2 minutes in a vacuum maintained at 2 X 10' And a non-porous titanium plating on iron is obtained. This plating endured 0.5N1-1CL test for a week.

EXAMPLE 26: ZIRCONIUM PLATlNG Colloidal zirconium hydride particle is used as the same process mentioned above. By heat treatment at 850C for 2 minutes non-porous zirconium plating is obtained. This zirconium plating also endured 0.5NHC1 test for a week.

lclaim:

l. A process for producing non-porous full-density metal articles comprising forming a porous compact of colloidal substantially pure metal particles having a maximum mean particle size of 0.2 micron, said metal being at least one metal selected from the group consisting of silver and the metals of groups lllb, lVb, Vb, and Vlll of the Periodic Table of the Elements through element No.92, and then sintering said porous compact at a temperature substantially below the melting point of said metal and thereby forming a full-density metal article within 10 minutes of the initiation of sintering, and maintaining said porous metal compact in a vacuum or an inert atmosphere until said full-density metal article is formed.

2. The process of claim 1, wherein said metal is at least one metal selected from the group consisting of the metals of groups lllb, Nb and Vb of the Periodic Table of the Elements, and wherein said colloidal metal particles are produced by thermally dehydrogenating the stoichiometric hydride of said metal; and wherein said sintering is in an atmosphere selected from argon and a vacuum having a pressure of less than 1 X 10- mm. of mercury.

3. The process of claim 2, wherein said metal is selected from the group consisting of titanium, zirconium, and tantalum.

4. The process of claim 2, wherein said colloidal metal particles are produced by dehydrogenating TiH and wherein said sintering is at a temperature of at least 1,100C.

5. The process of claim 4, wherein said sintering is at a temperature of about 1,200C.

6. The process of claim 4, wherein said titanium particles have a mean particle size of about 0.08 micron.

7. The process of claim 2, wherein said colloidal metal particles are produced by dehydrogenating Zrl-l 8. The process of claim 7, wherein said sintering is at a temperature of about l,500C.

9. The process of claim 2, wherein said metal is a lanthanide series metal.

10. The process of claim 2 wherein said metal is an actinide series metal.

ll. The process 'of claim I, wherein said metal is selected from the group consisting of iron, cobalt and nickel; wherein said metal particles are produced by reduction of the carbonyl of said metal; and wherein said sintering is in an inert gas or in a vacuum having a pressure of less than 1 X 10" mm. of mercury.

12. The process of claim 11, wherein said metal is iron.

13. The process of claim 11, wherein said metal is nickel.

14. The process of claim 1, wherein said metal is silver. 

1. A process for producing non-porous full-density metal articles comprising forming a porous compact of colloidal substantially pure metal particles having a maximum mean particle size of 0.2 micron, said metal being at least one metal selected from the group consisting of silver and the metals of groups IIIb, IVb, Vb, and VIII of the Periodic Table of the Elements through element No.92, and then sintering said porous compact at a temperature substantially below the melting point of said metal and thereby forming a full-density metal article within 10 minutes of the initiation of sintering, and maintaining said porous metal compact in a vacuum or an inert atmosphere until said full-density metal article is formed.
 2. The process of claim 1, wherein said metal is at least one metal selected from the group consisting of the metals of groups IIIb, IVB and Vb of the Periodic Table of the Elements, and wherein said colloidal metal particles are produced by thermally dehydrogenating the stoichiometric hydride of said metal; and wherein said sintering is in an atmosphere selected from argon and a vacuum having a pressure of less than 1 X 10 4 mm. of mercury.
 3. The process of claim 2, wherein said metal is selected from the group consisting of titanium, zirconium, and tantalum.
 4. The process of claim 2, wherein said colloidal metal particles are produced by dehydrogenating TiH2.00 and wherein said sintering is at a temperature of at least 1,100*C.
 5. The process of claim 4, wherein said sintering is at a temperature of about 1,200*C.
 6. The process of claim 4, wherein said titanium particles have a mean particle size of about 0.08 micron.
 7. The process of claim 2, wherein said colloidal metal particles are produced by dehydrogenating ZrH2.00.
 8. The process of claim 7, wherein said sintering is at a temperature of about 1,500*C.
 9. The process of claim 2, wherein said metal is a lanthanide series metal.
 10. The process of claim 2 wherein said metal is an actinide series metal.
 11. The process of claim 1, wherein said metal is selected from the group consisting of iron, cobalt and nickel; wherein said metal particles are produced by reduction of the carbonyl of said metal; and wherein said sintering is in an inert gas or in a vacuum having a pressure of less than 1 X 10 4 mm. of mercury.
 12. The process of claim 11, wherein said metal is iron.
 13. The process of claim 11, wherein said metal is nickel. 